1. Field of the Invention
Exemplary aspects of the present invention relate to a developing unit and an image forming apparatus, and more particularly to a developing unit for developing a latent image on an image carrier with toner and an image forming apparatus including the same.
2. Description of the Related Art
According to related arts, it is known that a developing unit transports toner to a developing area along with a rotary motion of a toner carrier while an electric field curtain generator provided on the toner carrier generates an electric field curtain which causes toner carried on a surface of the toner carrier to hop.
In such a related art developing unit, a spare charging roller is provided in a manner such that it abuts the toner carrier surface so that the electric field curtain effect stably acts upon the toner carried on the toner carrier surface.
The spare charging roller performs frictional charging on the toner between the spare charging roller and the toner carrier. Thereby, sufficiently charged toner having received the effect of electric field curtain is stably transported to the developing area.
Furthermore, it has been proposed that in a developing apparatus, toner is transferred from a developer carrier to one end surface of a transportation substrate (toner carrier) including a plurality of electrodes. The plurality of electrodes generates an electric field for transporting the toner by causing toner to hop by an electrostatic force. Such a developing apparatus transports the toner, which is transferred from the developer carrier, to the developing area across from a latent image carrier by the electrostatic force while causing the toner to hop on the transportation substrate.
Related art developers cause toner to hop by generating an electric field on a surface of a toner carrier. In order to cause the toner to hop, a weak adherence between the toner carrier surface and the toner may be important. It may also be important to generate an appropriate electric field on the toner carrier surface.
However, in the related art developing apparatuses, there is such a problem that toner may be adsorbed to the toner carrier surface. Consequently, toner may not be able to stably hop in the electric field generated on the toner carrier surface.
The main cause of this problem may be that some kind of external force acts on toner, thereby increasing the adhesion of toner relative to the toner carrier surface beyond the level of an electrostatic force from the electric field.
When the spare charging roller performs the frictional charging on the toner on the toner carrier surface, the toner is pressed against the toner carrier surface causing the adherence of the toner relative to the toner carrier surface to increase. Consequently, there may be such a problem that toner may not be able to stably hop.
Furthermore, when the external force continues to act on the toner carrier surface, the toner may be firmly fixed to the toner carrier surface. In such a case, the adhered toner may disrupt the electric field. Consequently, toner may not be able to stably hop.
When the electric field generated on the toner carrier surface is increased, the adherence of toner to the toner carrier surface may increase, thereby making it possible to cause the toner to hop. However, in such a case, when the toner affected by the increased electric field may be easily separated from the toner carrier surface. Consequently, stable toner hopping may not be able to achieve.